>^,&au.^..ML 


UBRARt 
STATE  PLANT  BOARP 


Issued  April  22.  1911. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— CIRCULAR  No.  133. 

L.  O    HOWARD.  Entomologist  and  Chief  of  Bureau. 


THE  ALFALFA   CATERPILLAR 


BT 


V.  L.  WILDERMUTII, 

Agent  and  Expert. 


WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :  1011 

84054°— Cir.  133—11 


I 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Mablatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  HuNTEB,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  cliarge  of  cereal  atid  forage  insect  investigations. 

A.  L.  QuAiNTANCE,  in  charge  of  deciduous  fruit  insect  investigations, 

E.  F.  Phillips,  in  charge  of  hee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 

RoLLA  P.  Curbie,  in  charge  of  editorial  work. 

Mabel  Colcord,  librarian. 

Cereal  and  Forage  Insect  Investigations. 

F.  ISI.  Webster,  in  charge. 

Geo.  I.  Reevf-S,  J.  A.  Hyslop,  W.  R.  Walton,  J.  T.  Monell,  V,  L.  Wildermuth, 

R.  A.  ViCKERY,  Herbert  T.  Osborn,  agents  and  experts. 
W.  J.  Phillips,  E.  O.  G.  Kelly,  Geo.  G.  Ainslie,  Philip  IjVGnsBU.L,  entomological 

assistants. 
A.  H.  Kirkland,  C.  N.  Ainslie,  T.  D.  Urbahns,  T.  H.  Parks,  E.  G.  Smyth, 

C.  W.  Creel,  H.  R.  Watts,  engaged  in  alfalfa  weevil  investigations. 
Nettie  S.  Klopfeb,  Ellen  Dashiell,  preparators. 
Miriam  Wells  Reeves,  collaborator. 
[Cir.  133] 
II 


Circular  No.  133.  Issued  April  22,  I9ii. 

United  States  Department  of  Agriculture, 

BUREAU  OF  ENTOMOLOGY. 
L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


THE  ALFALFA  CATERPILLAR. 

(Eurymus  curythcme  Boisd.) 

By  V.  L.  WiLDERMUTH,  Agcnt  and  Expert. 

INTRODUCTION. 

The  insect  under  consideration  in  this  circular  is  the  caterpillar 
(fig.  1)  of  one  of  our  most  beautiful  and  common  butterflies  (figs.  2, 
3)  belonging  to  the  group  known  as  "the  yellows,"  and  is  closely  re- 
lated to  the  well-known  cabbage  butterfly.  The  name  "  yellows  "  at 
once  gives  one  an  idea  of  the 
appearance  of  the  adult,  but 
this  may  be  misleading,  as  the 
species    is    polymorphic,    the 

coloration      varying      from      a        Fig.  1.— The  alfalfa  caterpillar  iEurymt4s  eury- 
briffht       yellow        (verv       fre-  theme)  -.   Larva    or    caterpillar    stage.     About 

^  *^      .       Tx        ,       "  twice  natural  size.      (Original.) 

quently  noticed),  through  an 

orange-sulphur  (the  most  commonly  noticed),  to  a  pale  white  (the 

least  often  noticed). 

For  some  years  past  the  green  caterpillars  of  this  butterfly  have 
been  reported  from  various  localities  in  the  southwestern  United 
States  as  feeding  on,  and  in  some  cases  doing  a  large  amount  of 
damage  to  growing  alfalfa  {Medicago  sativa).  It  should  be  men- 
tioned here  that  it  is  the  caterpillar  or  worm  stage  of  this  species  that 
does  the  damage,  and  not  the  adult  butterfly.  The  latter  feeds  on 
the  nectar  of  the  bloom  and  in  no  way  injures  the  plant.  In  fact,  the 
writer  has  noticed  these  butterflies  to  all  appearances  springing  the 
pollen  triggers  on  the  alfalfa  blossoms  while  feeding,  thus,  should 
his  observations  prove  correct,  benefiting  the  plant  for  seed  produc- 
tion.°     In  the  year  1906  a  correspondent  of  the  Department  of  Agri- 

^  Though  the  author  is  quite  confident  of  the  accuracy  of  his  observations,  it 
is  a  case  where  misconception  is  exceedingly  liable  to  occur ;  if  correct,  however, 
the  fact  is  entirely  new.  See  Dr.  I.  Urban,  Verhandlung  des  Botanischen 
Yereins  der  Provinz  Brandenberg,  1872,  p.  13;  Herman  Muller,  The  Fertiliza- 
tion of  Flowers,  par.  93  and  94,  1873 :  C.  V.  Piper,  Report  of  American  Breeders' 
Association,  1909,  Report  of  Committee  on  Breeding  Forage  Crops — F.  M. 
Webster. 

[Cir.  133]  1 


THE   ALFALFA   CATERPILLAR. 


culture  reported  the  caterpillar  infesting  the  lucern  fields  in  Big- 
horn County,  TTyo.,  and  in  the  year  1907  another  correspondent  re- 
ported it  as  a  "cutworm,"  damaging  the  alfalfa  at  Hanford,  Cal. 
This  caterpiHar  is  also  knoAvn  to  have  injured  alfalfa  in  Utah.  In 
1909  Mr.  C.  N.  Ainslie,  of  tlie  Bureau  of  Entomology,  found  tha  eggs 

and  larva?  of  this 
species  on  alfalfa  at 
Springer,  X.  Mex., 
but  doing  no  appar- 
ent damage.  In  the 
same  year  Mr.  E.  O. 
G.  Kelly,  ivlso  of  the 
Bureau  of  Entomol- 
ogy, found  the  larvae 
feeding  on  alfalfa  at 
Wellington,  Kans. 
In  Arizona,  in  the 
Salt    River    Valley 

Fig.  2.— The  alfalfa  caterpillar  {EitruinKs  curi/theme)  :  '^^^  ^^  ^'^^  1  Uma 
Female  in  the  adult  or  butterflj^  stage.  One-half  en-  ValleV,  farmers  Say 
larged.      (Original.)  ^j^^^   ^^    .^^    average 

about  one  j^ar  in  every  three  or  four  the  "  worms  "  become  sufficiently 
numerous  to  cause  considerable  damage.  In  the  Sacramento  Valle}^, 
and  in  the  irrigated  alfalfa  regions  of  south-central  California, 
according  to  Mr.  W.  E.  Packard,  of  the  California  Agricultural 
Experiment  Station,  the  butterflies  are  quite  numerous  during  certain 
years  and  cause  more  or  less 
damage. 

However,  not  until  alfalfa 
began  to  be  widely  grown  in 
the  newly  irrigated  region 
in  the  Imperial  Valley  of 
southern  California  did  the 
butterfly  assume  such  pro- 
portions, and  appear  with 
such  regularity  each  season, 
as  to  become  a  dread  to 
the  farmers,  particularly  to 
those  confining  their  efforts 
wholly  to  alfalfa  growing. 
It  was  in  1909,  after  a  season  when  the  larvae  had  taken  all  of  one 
crop  of  hay,  causing  a  loss  of  hundreds  of  dollars  on  his  320-acre 
ranch,  as  well  as  a  similar  loss  to  dozens  of  other  ranchers  in  the 
valley,  that  Mr.  J.  A.  Walton,  of  the  Imperial  Valley,  wrote  the 
United  States  Department  of  Agriculture  asking  for  a  remedy  or  a 

[Clr.  I'M] 


Fu;.  ."..The  alfalfa  <'ati'r|)illar  {IJiirymus 
vurythcmc)  :  Male  In  the  adult  or  butterfly 
static     One-half  enlarged. 


(Original.) 


THE   ALFALFA   CATERPILLAR.  6 

method  of  dealing  with  the  pest.  As  no  remedy  was  known,  plans 
were  at  once  begun  for  investigating  the  outbreak  and  if  possible 
working  out  some  plans  of  controlling  the  same. 

This  circular  is  a  partial  report  of  the  work  done  by  the  writer  in 
the  Imperial  Valley  the  past  season  (1910),  and  while  the  investi- 
gation is  still  under  way,  another  year  being  necessary  to  complete  the 
same,  it  is  thought  desirable  to  give  to  the  farmers  in  the  alfalfa- 
growing  section  of  the  country  the  information  secured,  it  being  of 
such  a  nature  as  to  be  of  great  immediate  benefit,  if' put  to  practical 
use,  in  controlling  the  pest. 

DISTRIBUTION. 

According  to  Scudder,  this  species  is  more  especially  a  western 
insect,  being,  as  a  rule,  much  more  abundant  west  of  the  Mississippi 
River  than  east  of  it,  and  although  its  range  extends  eastward  it  is 
rather  rarely  found  east  of  the  Allegheny  Mountains.  In  the  AYes-t  it 
occurs  from  Mexico  northward  into  the  Dominion  of  Canada,  thus 
covering  the  chief  alfalfa-growing  section  of  the  United  States.  It  is 
especially  abundant  throughout  the  regions  where  irrigation  is  most 
extensively  followea. 

DESCRIPTION  OF  THE  SPECIES. 

A  meager  description  is  given  here  of  the  various  stages  of  develop- 
ment, in  order  to  enable  the  casual  observer  to  recognize  the  different 
forms : 

The  adult  (figs.  2,  3). — The  wings  of  the  adults  vary  in  color  from 
yellow  to  white,  being  usually  a  sulphur-yellow  above,  with  black 
outer  margins,  a  conspicuous  black  spot  in  the  center  of  each  fore 
wing,  and  a  faint  yellowish  spot  in  the  center  of  each 
hind  wing.  The  underside  of  the  wings  is  of  a  lighter 
shade  than  the  upper  surface  and  is  the  side  noticed 
when  the  butterfly  is  at  rest  with  its  wings  folded 
above  its  back.  The  wing  expanse  is  nearly  2  inches ; 
in  some  it  is  a  little  less  than  this  and  in  a  few  a 
little  more. 

The  egg.— The  eggs  (fig.  4)  are  small,  only  0.06  fig.4.— Theaifaifa 
inch  long,  with  from  18  to  20  slightly  raised  longitu-  o^reltij  eniargfl 
dinal  ridges  or  ribs,  broken  by  cross  lines.  They  are  (Redrawn  from 
elongated,  white  when  laid,  but  turning  reddish 
brown  after  the  second  day,  and  are  deposited  upright,  with  the 
basal  end  attached  usually  to  the  upper  surface  of  the  leaf.  They 
are  always  deposited  on  fresh,  green  alfalfa,  and  never  on  dry  or 
partially  matured  alfalfa. 

The  larva. — The  full-grown  larva  (fig.  1)  is  usually  1  inch  long, 
sometimes  a  little  over,  dark  green  in  color,  with  a  white  stripe  on 

[Cir.  133] 


THE   .YLFALFA   CATERPILLAR. 


each  side,  partially  bn>ken  by  black  and  red  dots  at  each  spiracle. 
There  is  often  an  intermediate,  narrower,  and  less  distinct  white  line 
just  above  each  of  the  lateral  lines.  In  some  specimens  a  black  or 
dark-green  median  dorsal  line  is  also  present. 

The  pupa. — The  pupa  (fig.  5)  is  yellowish  green,  has  no  cocoon, 
and  is  found  head  end  up.  attached  b}^  two  threads,  one  of  them  form- 
ing a  swing,  to  an  alfalfa  stalk, 

INVESTIGATIONS  IN  THE  IMPERIAL  VALLEY  OF  SOUTHERN   CALIFORNIA. 

The  investigations  were  begun  by  the  author  about  the  middle  of 
March,  1010,  and  carried  on  through  the  summer  until  late  in  the  fall 
of  the  same  year.  The  writer  was  at  first  located  on  the  J.  A.  Walton 
ranch,  in  the  extreme  southeastern  part  of  the  valley,  and  later  at 
El  Centro,  where  the  work  was  carried  on  in  cooperation  with  Mr. 
Walter  E.  Packard,  an  agent  of  the  California 
Agricultural  Experiment  Station,  to  whom  a  great 
amount  of  credit  is  due  for  the  assistance  and  timely 
suggestions  offered. 

The  Imperial  Valley  is  a  place  unique  in  location 
and  altitude.  It  is  an  irrigated  region  entirely  sur- 
rounded by  mountains  and  desert.  The  major  part 
of  the  valley  lies  below  sea  level — some  of  it,  in  fact, 
as  much  as  250  feet  below.  The  weather  is  warm 
most  of  the  year  and  hot  the  rest  of  the  year.  It 
hardly  ever  rains,  and  the  humidity  is  usually  very 
low.  The  growing  season  extends  over  practically 
the  entire  year,  there  being  an  entire  lack  of  freez- 
ing weather  during  some  winters.  On  the  average 
there  is  not  during  the  year  more  than  one  month 
of  weather  that  could  be  called  winter  weather. 

The  conditions  just  referred  to  serve  to  explain 
the  innnense  numbers  of  these  butterflies  in  the  val- 
ley. The  period  over  which  the  butterflies  are  able  to  continue 
breeding  Avithout  being  molested  is  very  long,  being  from  March  to 
December.  Then,  too,  owing  to  the  very  low  humidity  there  is  usu- 
ally insufficient  moisture  to  permit  the  development  of  whnt  api^eared 
to  be  a  contagious  disease,  resembling  in  effect  flacJwr'w  of  the  silk- 
wonn.  This  disease  was  found  to  be  largely  responsible  for  keei)ing 
this  butterfly  in  check  in  other  parts  of  the  State  of  California  and 
in  southern  Arizona. 


Fig.  5.— The  alfalfa 
caterpillar  (Fury- 
mus  curythetne)  : 
Pupa  or  chrysalis 
stage.  Twice  nat 
ural  size.  (Origi- 
nal.) 


SEASONAL   HISTORY    IX    THE    IMPERIAL   VALLEY. 

On  the   U)i\\  of  Marcli.   1910,  several   adult   individuals,  possibly 
adults  that  had  issued   from  hibernating  pupa*,  were  caught   in  (he 
act  of  flying  over  alfalfa   (ields  and  placed   in  a  large  mosqui(()-b:n* 
(cir.  L-;:'.i 


THE  ALFALFA   CATERPILLAB.  5 

cage  which  covered  an  alfalfa  plant.  These  immediately  deposited 
eggs.  It  can  be  said,  therefore,  that  the  hibernating  forms  issue 
between  March  1  and  March  20.  The  season  of  1909-10  was  ex- 
ceedingly cold  in  the  valley,  while  that  of  1910-11  was,  up  to  the 
middle  of  February,  precisely  the  reverse,  and  up  to  the  8th  of  this 
month  larvae  had  been  found  present  in  limited  numbers  in  the 
fields.  It  seems,  therefore,  probable  that  during  some  winters  the 
species  may  breed  throughout  the  entire  season,  as  sometimes  there 
is  hardly  a  frost.  Either  the  larval  or  pupal  stage,  or  both  stages, 
would  during  such  winters  be  merely  lengthened,  for  that  is  really 
what  happens  in  the  spring  or  fall  of  the  year,  and  thus  the  insect 
could  hardly  be  said  to  hibernate.  However,  eggs  were  being  laid 
on  March  15,  and  possibly  a  few  days  earlier,  and  these  gave  rise 
to  the  first  or  spring  generation.  This  generation  was  very  slow  in 
developing,  requiring  about  44  days,  the  egg  stage  being  6  days,  the 
larval  stage  30  days,  and  the  pupal  stage  8  days.  As  the  weather 
became  warmer  each  of  these  periods  gradually  lessened  until  in  the 
third  generation  only  22  days  were  required  for  complete  develop- 
ment, the  egg  stage  in  this  case  being  4  days,  the  larval  stage  12  days, 
and  the  pupal  stage  5  days.  These  were  the  periods  of  development 
for  individuals  confined  in  cages;  in  the  field  a  few  days  longer, 
often  as  many  as  four  or  five,  seemed  to  be  required  for  development 
from  egg  to  adult. 

The  first  generation  covered  the  period  from  March  15  to  April 
30;  the  second  generation  from  May  1  to  May  28;  the  third  genera- 
tion from  May  28  to  June  20;  and  the  fourth  generation  from  June 
20  to  July  15.  There  were  thus  four  distinct  generations,  the  last 
being  less  distinct  than  the  others.  Later  in  the  year  the  generations 
became  so  largely  confused  that  it  was  impossible  to  separate  them. 
Just  as  the  fourth  generation  was  beginning  to  pupate,  the  supposedly 
contagious  disease  before  mentioned  killed  a  large  majority  of  the 
larvae  present  at  the  time,  and  thus  observations  along  life-history 
lines  were  checked.  From  this  time  on,  scattering  individuals  pro- 
duced eggs  and  gradually  increased  in  numbers  up  to  October,  after 
which  time  quite  a  few  worms  were  present  in  some  fields,  and  often 
considerable  damage  was  noted.  In  fields  that  had  been  green  dur- 
ing August,  when  the  water  supply  was  short  in  the  valley,  there 
were  always  more  of  these  caterpillars  noticed  than  there  were  in 
fields  that  had  not  been  green  during  the  month  stated.  This  was 
due  to  the  fact  tliat  the  worms  were  able  to  feed  in  these  green  fields, 
and  therefore  in  the  fall  there  remained  quite  a  number  of  adults. 
By  the  middle  of  October,  as  the  nights  became  cool,  .the  larvae  and 
pupae  did  not  develop  as  rapidly  as  during  the  summer  months,  and 
the  species  just  held  its  own  in  num.bers  up  to  December  28,  1910, 
when  all  were  in  the  hibernating  stage. 

[Cir.  133] 


6  THE   ALFALFA   CATERPILLAR. 

TWO  CLASSES  OF  RANCHES PASTCRE  RANCHES  AND  HAY  RANCHES. 

The  alfalfa  ranches  in  the  Imperial  Valle}^,  Cal.,  can  all  be  divided 
into  two  classes:  (1)  Pasture  ranches,  or  those  devoted  entirely  to 
the  fattening  or  pasturing  of  cattle  and  hogs,  and  (2)  hay  ranches, 
or  those  on  which  the  crop  is  utilized  for  hay.  For  convenience  we 
can  look  at  these  separately. 

Pasture  ranches. — It  was  noticed  early  in  the  summer,  and  the 
writer's  attention  was  called  to  the  fact  by  a  number  of  farmers, 
that  ranches  devoted  to  the  raising  of  stock,  either  cattle  or  hogs, 
were  rarely,  if  ever,  seriously  affected  by  the  pest.  On  some  dozen 
sucii  ranches  visited  and  inspected  very  few  worms  could  be  found, 
and  the  butterflies  flying  over  the  fields  were  never  numerous.  At  first 
this  was  considered  entirely  due  to  the  fact  that  there  was  hardly  ever 
any  bloom  present  for  the  adults  to  feed  upon  and  that  the  greater 
part  of  the  fields  was  kept  grazed  quite  closely,  making  the  condi- 
tion in  pastured  fields  less  favorable  for  the  laying  and  development 
of  the  eggs.  Under  such  conditions  the  number  of  eggs  deposited 
is  greatly  reduced.  Man}^  of  the  eggs  laid  on  the  young  growth 
under  such  conditions  are  destroyed  by  the  grazing  of  the  stock,  and 
the  percentage  that  develops  is  kept  to  a  minimum.  Later  in  the 
season  it  was  noted  that  on  the  stock  ranches  visited  the  disease 
l^reviously  mentioned,  which  is  common  to  lepidopterous  larvae,  was 
more  prevalent  than  on  hay  ranches.  All  the  factors  determining 
this  difference  have  not  been  ascertained,  but  the  fact  itself  is  quite 
significant. 

On  some  of  the  ranches  coming  under  the  writer's  observation  the 
alfalfa  was  allowed  to  grow  for  some  four  weeks,  or  until  it  reached 
the  height  of  about  20  to  24  inches.  Cattle  were  then  turned  into  the 
field,  and  within  a  few  days  the  alfalfa  became  trampled.  The 
ground  and  the  alfalfa  were  very  moist,  there  being  more  or  less 
dew  present  ever}^  morning,  and  droppings  from  the  cattle  and  hogs 
naturally  brought  about  a  foul  condition  in  the  field,  assisting  in  the 
retention  of  moisture.  AVhether  as  a  result  of  these  conditions  or  as 
a  coincidence,  the  contagious  disease  appeared  to  the  writer  to  be 
much  more  prevalent  in  these  fields  than  elsewhere. 

Ilay  randies. — It  is  on  ranches  and  fields  from  which  successive 
crops  of  hay  are  taken  that  the  height  of  the  damage  is  reached.  In 
such  fields  the  conditions  for  the  development  of  the  species  are  as 
nearly  ideal  as  possible,  and  here  the  worms  are  ordinarily  unmo- 
lested in  their  feeding  and  growth.  The  period  elapsing  from  the 
time  that  one  crop  is  cut  until  another  is  ready  to  harvest  so  nearly 
coincides  with  the  length  of  the  i)erio(l  necessary  for  the  develop- 
ment of  any  one  generation  of  the  butterfly  that  the  cutting  of  the 
hay,  as  ordinarily  carried  on,  does  not  reduce*  their  numbers  or  dis- 
turb their  work,  since  the  worm  will  likely  be  in  the  advanced  stage 
[Cir.  mm 


THE   ALFALFA    CATERPILLAR.  7 

or,  perhaps,  have  passed  into  the  pupal  stage  before  the  crop  is 
cut  off. 

Many  fields  observed  by  the  writer  were  attacked  in  strips  or 
patches.  Sometimes  one  border  would  be  almost  totally  devoured, 
while  an  adjoining  plot  would  not  be  molested.  Again,  in  other 
fields  irregular  patches  would  be  attacked  and  the  rest  of  the  field 
not  materially  injured.  In  cases  where  whole  borders  of  alfalfa 
were  injured,  the  time  and  amount  of  water  applied  in  irrigating 
produced  an  uneven  growth,  and  as  the  generation  of  butterflies,  on 
issuing,  chose  for  egg-laying  the  strip  that  was  the  greenest  and 
freshest,  this  strip  would  be  the  one  damaged.  It  seems  possible  to 
account  for  the  irregular  patches  in  the  same  way — that  is,  consider- 
ing that  these  patches  were  ones  that  were  held  back  because  of  the 
condition  of  the  soil.  Tlie  soil  conditions  in  one  part  of  the  field 
may  be  quite  different  from  those  in  another  part  of  the  same  field, 
and  thus  a  varying  growth  of  the  crop  results,  which  would  be  at- 
tacked in  patches. 

FOOD  PLANTS. 

Besides  alfalfa  the  larva  is  known  to  feed  upon  the  tAvo  buffalo 
clovers,  TrifoUum  reflexum  and  T.  stolonifcriim^  which  probably  con- 
stitute its  original  native  food  plants.  It  also  feeds  upon  white  clover 
{T.  repens)^  and  in  California  on  T.  tridentatuw^  but  is  said  not  to 
attack  red  clover  {T.  pratense).  Other  food  plants  noted  by  Scudder 
are  Ilosackia,  ground  plum  {Astragalus  caryocarpus)^  and  A,  crotal- 
arice.  The  butterfly  is  known  to  oviposit  on  Medicago  hispida^  and  at 
Indio,  Cal.,  on  July  1  the  writer  found  larva3  feeding  on  sweet  clover 
{Melilotus  alba),  which  strangely  enough  they  seemed  to  prefer  to  a 
patch  of  alfalfa  growing  close  by.  Eggs  were  also  observed  to.be 
very  numerous  upon  the  leaves  of  the  sweet  clover  at  the  same  time. 

INSECT   ENEMIES. 

The  white  eggs  of  tachinid  flies  were  always  in  evidence  Avherever 
any  larvae  were  to  be  found,  and  the  young  of  these  destroy  quite  a 
large  number  of  worms.  In  one  instance  it  was  noted  that  as  many  as 
15  per  cent  of  the  worms  had  tachinid  eggs  on  them.  Because  of  the 
supposedly  contagious  disease,  as  shown  in  a  following  paragraph, 
little  success  resulted  from  rearing  these  parasitic  flies.  Five  speci- 
mens were  reared  from  the  larvaB  of  Eurymus.  These  were  all  of  the 
species  Euplwi^ocera  daripennis  Macq.  (fig.  6).  One  specimen,  de- 
termined by  Mr.D.W.  Coquillett,of  this  bureau,  as  Masicera  sp.,  was 
reared  from  the  pupa  of  Eurymus. 

Two  species  of  hymenopterous  parasites  were  reared.  From  the 
Eurymus  larvae  several  specimens  of  Llmnerhimsp. — all  females,  how- 

[Cir.  133] 


8 


THE    ALFALFA    CATERPILLAR. 


ever — were  reared,  while  one  specimen  of  Chalets  ovata  Say  (fig.  7) 
was  reared  from  a  pupa  of  Eiir^'mus.     It  seems  from  this  that  the 

hymenopterous    parasites 


^--^ 


Fig.  6. — Euphoroccra  cUiripennift,  a  parasite  of  the 
alfalfa  caterpillar  :  Adult  and  enlarged  antenna  of 
same;   puparium.      Enlarged.      (From  Howard.) 


are  much  in  evidence,  al- 
though if  the  material 
had  not  been  aifected  by 
the  supposedly  contagious 
disease  many  more  mi^ht 
have  been  secured. 

The  eotton  hollworm 
mistaken,  for  an  alfalfa 
caterpillar. — A  large 
green  caterpillar  known 
as  the  bollworm,  liello- 
this  ohsoleta  Fab.  (fig.  8), 
that  can  be  distinguished 
from  the  Eurymus  be- 
cause it  is  of  a  lighter 
green  color,  about  one- 
fourth   larger,    and    hairy    and    rough    in    appearance    rather   than 

smooth,  Avith  three  black  lines  traversing  its  body  lengthwise,  is  quite 

prevalent  in  the  Imperial  Valley,  and  is  often  mistaken   for  the 

alfalfa   caterpil- 

1  a  r   by   ma  ny 

farmers.     Mr. 

E.  O.  G.  Kelly 

and   Mr.   T.   H. 

Parks,  agents  of 

the.    Bureau    of 

Entomology, 

working  at  Wel- 

ington,  Kans.,  in 

the    summer    of 

1909   also  noted 

this  species  and 

reported     it     as 

being  of  a   pre- 

daceous     habit.** 

As  noted  in  the 

valley,    it   was 


found  to  do  very 

little  damage  to  alfalfa,  but  to  Ik 


Fig.    7. — Chalcis   ovata,   a   parasite   of   the   alfalfa   caterpillar: 
u.  Pupa  ;  h,  parasitized  pupa  of  tussock  moth   (Ilcincrocatnpa 
Icurontiijma)  :  c.  adult  ;  </,  same  in  profile 
Enlarged.      (From  Howard.) 


c.  pupal   exuvium. 


a  ravenous  enemv  o 


f  tl 


w  a 


falfa 


«Tliis  c;iiinn)alistic  habit  has  also  been  observetl  In  Texas  by  Quaintance  and 
Brues.     Bui.  50.  I'.iir.  Knt.,  U.  S.  Dept.  Ajrr.,  pp.  79-SO,  1JK>5. 
[Cir.  133] 


THE   ALFALFA   CATERPILLAR.  9 

caterpillar,  never  eating  alfalfa  as  long  as  it  could  find  the  larvae  or 
pupae  of  Eurymus  around. 

One  of  these  larvae  ate  5  larvae  of  the  Eurymus  during  a  single  day, 
and  on  May  25  the  writer  counted  many  dozens  of  pupal  cases  in  the 
field  that  had  the  contents  eaten  out.  Each  case  had  an  irregular 
opening  eaten  into  it;  sometimes  the  end  of  the  abdomen  would  be 
eaten  away,  and  again  the  opening  would  be  on  the  side,  often  the 
entire  side  being  destroyed.  Upon  further  search  the  larvae  of  Helio- 
this  were  found  in  the  act  of  devouring  the  pupae  and  were  thus 
responsible  for  the  damage. 

OTHER  NATURAL  ENEMIES. 

Larval  disease. — The  most  common  natural  enemy  observed  was  a 
supposedly  contagious  disease  w^hich  there  has  not  yet  been  an  oppor- 
tunity to  carefully  study.  This  was  prevalent  all  over  the  valley 
and  is  present  at  all  seasons.  It  destroys  both  the  pupa  and  larva, 
but  more  often  the  larva.  The  worms  when  attacked  by  the  disease 
turn  a  lighter  green,  become  sluggish,  and  in  a  day  or  two  are  nothing 
but  a  soft,  decayed  mass,  usually  found  hanging  to  the  alfalfa  stalks. 
The  development  of  the  disease  apparently  depends  upon  moisture, 
as  it  is  more  often  noticed  in  moist  fields.  The  fact  that  it  does  not 
at  all  times  keep  the  worms  in 
suppression  is  without  a  doubt 
due  to  the  fact  that  the  climate 
of  the  Imperial  Valley  is  very 
dry.     Larvae    brought    to    the  ,     ^ 

/^  .  Fif;.    S.— Bollworm    {Hcliothis    ohsoleta),    an 

laboratory  for  rearmg  ot  insect  enemy    of    the    alfalfa    caterpillar.     Twice 

parasites  and  for  life-history  ^^^"^^^  «^^^-  (Original.) 
studies  in  a  large  percentage  of  cases  died  of  the  disease  as  soon  as 
confined.  A  quantity  of  worms  sent  to  r>erkeley,  Cal.,  by  Mr.  AVilsie, 
of  the  Imperial  Valley  horticultural  commission,  for  experimental 
rearing  of  parasites,  all  died  of  the  disease,  either  before  reaching 
their  destination  or  the  day  after.  During  the  first  week  of  July  the 
humidity  was  exceptionally  high  for  the  Imperial  Valley,  and  at  the 
time  about  95  per  cent  of  the  larvae  in  the  valley  succumbed  to  disease, 
thus  saving  a  hay  crop  for  a  great  many  of  the  farmers,  but  stopping 
experiments  almost  completely.  It  is  probable  that  this  disease  has 
occurred  in  years  past,  and  it  may  occur  in  future  years,  at  some  time 
during  the  summer  season,  in  such  abundance  as  to  destroy  a  brood, 
as  it  did  in  the  past  year  (1910). 

It  seems  to  be  partly  due  to  this  disease  that  the  alfalfa  cater- 
pillar does  not  appear  in  such  large  numbers  in  other  regions  of  the 
vSouthwest,  notably  in  alfalfa  regions  in  Arizona.  Here  there  seems 
to  be  greater  humidity  and  more  moisture,  and  the  disease  is  able  to 
keep  the  number  of  worms  reduced  to  a  minimum. 

[Cir.  133] 


10  THE    ALFALFA    CATERPILLAR. 

It  is  the  intention  of  the  Bureau  of  Entomology  to  repeat  these 
observations  and  ex^^eriments  in  the  Southwest  during  the  summer  of 
1911,  and  in  order  to  do  so  the  bureau  would  be  glad  to  cooperate 
with  any  farmers  who  wish  to  put  their  farms  or  ranches  under  a 
rigid  S3^stem  of  control.  The  greater  the  number  of  farmers  follow- 
ing this  plan  the  greater  the  beneficial  results  that  may  be  expected. 

METHODS   OF   CONTROL. 
INSECTICIDES. 

In  dealing  v.  ith  insect  pests  affecting  cereal  and  forage  crops  it 
has  proved  possible  in  only  a  few  instances  to  control  them  by  the 
use  of  any  of  the  various  insecticides  or  poisons.  The  reason  for  this 
lack  of  success  lies  largely  in  the  fact  that  such  crops  are  distributed 
over  a  \Yide  area  and  the  expense  of  application  of  any  insecticide  as 
a  control  measure  is  necessarih^  bigh,  while  a  lack  of  thoroughness  is 
likely  to  arise  when  one  tries  to  keep  the  expense  of  treatment  down 
to  an  economical  basis. 

Since  the  alfalfa  hay  is  fed  to  stock,  it  is  not  possible  to  use  any 
of  the  arsenical  poisons  against  the  caterpillar  of  the  alfalfa  butter- 
fly. A  few  experiments  were  tried  by  using  pyrethrum  or  "  buhach." 
As  this  is  not  a  poison,  and  since  its  fatal  effect  upon  the  larvae  of 
butterflies  is  produced  externally  through  their  breathing  pores, 
there  would  thus  be  no  danger  to  stock.  Pyrethrum  was  used  in  one 
case  at  full  strength,  and  in  another  instance  it  was  diluted  with  equal 
proportions  of  flour.  An  aj:>plication  was  made  by  dusting  this  sub- 
stance from  a  cheesecloth  sack,  following  the  primitive  m.ethod  of 
ap})lying  Paris  green  to  potato  vines,  at  the  rate  of  :^  pounds  of 
pyrethrum  to  the  half  acre,  which  in  the  case  of  diluted  material 
would  make  IJ  pounds  of  pyrethrum  to  the  half  acre.  This  first 
test  was  tried  on  July  8,  and  no  results  were  obtained,  because  of  the 
fact  that  just  two  days  later  practically  all  of  the  worms  in  the  field 
where  the  test  was  being  made  were  destroyed  by  the  malady  before 
mentioned.  The  same  experiment  was  repeated,  however,  on  Septem- 
ber 22,  and  in  this  case  also  the  results  were  negative,  not  a  cater- 
pillar being  killed.  It  would  seem,  therefore,  that  the  application 
was  not  siifTiciently  heavy  to  kill  the  worms,  and  that  to  have 
increased  the  amount  of  pyrelhrum  applied  might  have  resulted  in 
the  eradication  of  the  pest;  but  as  the  cost  of  pyrelhnnn  at  the  rate 
of  3  pounds  to  the  acre  is  already  nearly  $2,  without  considering  the 
expense  of  application  by  hand,  this  would  be  out  of  consideration 
from  an  economic  point  of  view.  However,  the  excellent  results 
obtained  through  the  use  of  i)yrethruni  in  the  case  of  other  insects 
will  justify  further  experimentation  along  this  line,  and  it  may  be 
possible  to  use  it  in  the  smaller  fields. 
[(Mr.  i;:;{i 


THE   ALFALFA   CATERPILLAR.  11 

SYSTEM    OF   CROP    CULTURE, 

For  the  reasons  just  given  the  control  problem,  in  dealing  with 
this  alfalfa  pest,  resolves  itself  to  one  of  the  method  of  handling  the 
crop.  Xot  long  after  the  Bureau  of  Entomology  began  observations 
in  the  Imperial  Valley  the  writer  was  informed  by  well-to-do  ranchers 
that  not  all  alfalfa  fields  or  even  all  ranches  were  affected  by  the 
caterpillars,  there  being  apparently  certain  conditions  regulating  the 
devastation.  One  cause  for  this,  as  noted  earlier  in  tliis  paper,  was 
the  presence  of  stock  in  certain  fields,  but  even  in  hay  ranches  there 
was  a  variation  in  the  numbers  of  the  caterpillars.  Accordingly 
there  was  outlined  a  series  of  experiments  in  which,  in  certain  fields 
under  observation,  definite  methods  of  management  were  tested  to 
see  whether  some  of  them  would  not  reduce  or  perhaps  entirely  elimi- 
nate the  damage.  Before  describing  the  conditions  existing  in  these 
fields  it  would  be  well  to  consider,  first,  the  conditions  existing  in 
certain  other  alfalfa  fields  not  under  the  direction  of  the  agents  of 
the  bureau  which  suffered  gi-eatly  because  of  the  pest,  the  owners 
often  losing  an  entire  crop.  The  first  fact  noted  was  that  the  cater- 
pillar damage  in  such  fields  seemed  to  be  correlated  with  the  condi- 
tion of  the  soil.  A  field  serioush'  damaged  often  revealed  a  poor 
soil ;  at  least,  a  soil  not  well  adapted  to  alfalfa  culture,  and  conse- 
quently producing  a  slow-growing  crop.  Of  course,  not  all  the  fields 
damaged  were  of  such  poor  soil,  for  some  of  the  very  best  alfalfa 
fields  were  seriously  ravaged,  but  in  these  latter  cases  this  was  at- 
tributable to  other  factors,  such  as  time  and  careless  manner  of  cut- 
ting and  time  of  irrigation.  The  sandy  loams  or  light  soils  are  the 
best  for  alfalfa  production,  and  consequently  least  damaged.  A 
heavy  soil  can  be  greatly  improved  and  the  growth  of  the  alfalfa 
increased  by  deep  plowing  and  thoroughly  preparing  the  seed  bed 
at  time  of  seeding  the  crop  and  then  renovating  the  alfalfa  yearly  by 
disking  or  by  the  use  of  an  alfalfa  renovator. 

The  worst  conditions  noted  were  those  in  which  the  attack  of  the 
caterpillar  was  due  to  delayed  cutting  of  the  hay  crop  and  due  quite 
often  to  the  fact  that  many  of  the  ranchers  were  trying  to  cultivate 
more  land  than  it  is  possible  for  one  man  to  farm  successfully.  With 
such  ranchers  some  of  the  following  defects  are  observable  in  their 
treatment  of  the  hay  crop:  First,  there  is  often  insufficient  water 
used  to  provide  for  the  prompt  development  of  the  alfalfa  crop.  An 
abundance  of  water  is  very  necessary,  as  it  enables  the  alfalfa  to  make 
faster  growth,  and  thus  the  farmer  can  reap  his  crop  sooner  and  be- 
fore the  caterpillars  have  effected  much  damage.  Second,  the  crop 
is  not  cut  early  enough  in  the  majority  of  cases — about  90  per  cent — 
that  is,  the  alfalfa  is  too  far  advanced  in  bloom  when  cut,  and  this 
delayed  cutting  enables  the  caterpillars  to  mature  successfully.     The 

[Cir.  133] 


12  THE   ALFALFA    CATERPILLAR. 

alfalfa  should  be  cut  just  when  it  is  beginning  to  bloom.  Other 
noticeable  factors  which  tended  to  hamper  control  measures  were  that 
at  haying  time  the  crop  was  cut  high,  the  turning  corners  were  left 
ragged,  and  the  ditch  banks  and  borders  poorly  mowed,  if  at  all,  and 
thus  the  caterpillars  that  were  present  and  had  not  gone  through  to 
the  adult  stage  had  a  large  amount  of  material  upon  which  to  de- 
velop, and  soon  did  so,  so  that  the  butterflies  from  these  were  ready 
for  the  next  crop.  These  places  would  also  afford  bloom  which  would 
naturally  attract  the  butterflies. 

P'or  fields  in  which  good  cultural  conditions  were  to  be  created  and 
in  which  methods  were  to  be  inaugurated  that  would  not  further  the 
development  of  the  caterpillars,  10  locations  were  selected  and  used 
as  a  basis  of  work.  From  what  was  said  in  the  previous  paragraph 
it  will  be  readily  seen  that  the  thing  to  be  done  in  these  fields  was  to 
put  them  under  a  system  that  would  remedy  all  or  part  of  the  defects 
noted  in  other  fields. 

As  has  been  mentioned  before  in  this  paper,  four  generations  of 
caterpillars  were  observed  in  the  Imperial  Valley  the  past  year 
(1910).  A  large  part  of  the  damage  was  due  to  the  caterpillars  of 
the  third  and  fourth  generations,  the  first  and  second  not  being 
numerous  enough  to  assume  any  serious  aspect.  The  task,  then,  was 
to  keep  their  numbers  below  the  point  at  which  they  could  do  any 
considerable  damage.  The  time  to  start  this  control  work  was  natur- 
ally with  the  earlier  generations.  The  ten  fields  mentioned  (no  two 
of  which  had  had  the  same  conditions  of  culture  previous  to  that 
year,  and  which  had  all  suffered  more  or  less  damage  the  year  before, 
namely,  in  1909)  were  given  Avhat  might  be  termed  clean  culture,  or 
careful  management.  Just  as  soon  as  possible  after  removing  a  crop 
of  hay,  using  the  methods  to  be  described  later,  the  field  was  irrigated 
thoroughly,  thus  starting  the  growth  quickly.  The  field  was  again 
irrigated  as  soon  as  the  dry  condition  of  the  crop  required,  and  thus 
the  growth  was  forced  and  not  allowed  to  be  checked.  It  takes  about 
28  days  to  produce  a  hay  crop  in  the  Imperial  Valley,  a  little  longer 
than  this  in  the  spring  and  fall,  and  a  few  days  less  in  warmer 
weather.  It  also  takes  just  as  many  days  as  has  been  shown  under 
"  seasonal  history  "  for  the  butterflies  to  develop  from  egg  to  adult. 
Now  if  the  crop  of  hay  be  forced  by  frequent  watering,  or  because 
of  good  soil  conditions,  the  worms  will  not  have  gone  into  the  rest- 
ing stage  at  time  of  cutting,  but,  instead,  will  still  be  feeding  on  the 
green  jilfalfa,  and  when  the  hay  is  cut  and  removed  conditions  are 
rendered  unfavorable  for  their  development  and  their  food  supply 
will  be  correspondingly  reduced.  Therefore,  the  hay  should  be  cut 
just  as  it  is  coining  into  bloom,  which  is  a  few  days  sooner  than  it 
is  generally  thought  advisable  to  cut  it,  as  a  generation  of  worms 
will  take  a  whole  field  in  a  short  time.    Thus  not  only  will  the  hay 

[Clr.  i;i3] 


THE   ALFALFA    CATERPILLAR.  13 

be  saved,  but  the  major  portion  of  the  larvae,  finding  a  lack  of  the 
food  necessary  for  their  complete  development,  will  ultimately  perish. 
To  bring  about  this  condition,  however,  it  is  necessary  to  mow  the 
field  carefully,  leaving  no  high  stubble.  The  turnrows,  borders, 
and  ditch  banks  should  also  be  closely  mown,  as  this  will  not  only 
reduce  the  supply  of  food  for  the  larvae  but  also  that  of  the  butter- 
flies, as  such  plants  will  afford  considerable  bloom.  In  two  cases  in 
the  writer's  experiments  it  became  necessary  to  remow  the  fields 
at  a  cost  of  from  30  to  50  cents  per  acre,  and  then  in  all  cases  to 
irrigate  promptly.  As  a  result  of  this  procedure  a  large  percentage 
of  the  caterpillars  failed  to  develop  to  the  imago  or  butterfly  stage. 
Deducting  these,  together  with  the  larger  number  that  failed  to 
reach  the  pupal  stage,  it  will  be  seen  that  there  were  many  hundred 
less  worms  to  attack  the  next  crop,  as  each  butterfly  developing  from 
them  would  have  deposited  at  least  100  eggs.  In  some  fields,  in- 
stead of  irrigating  immediately  after  the  hay  was  removed,  the 
experiment  was  tried  of  letting  the  field  go  dry  for  several  days, 
and  thus  starving  the  worms,  AMiile  this  gave  good  results  it  was 
not  as  satisfactory  as  the  method  of  immediate  irrigation,  for  there 
was  always  enough  moisture  in  the  field  to  start  the  new  crop  going 
and  thus  provide  a  little  food  for  the  caterpillars. 

The  complete  success  of  these  methods  is  dependent  on  cooperation 
among  the  farmers,  for  the  larger  the  percentage  of  those  who  in- 
augurate a  good  cultural  system  the  greater  will  be  the  benefit  derived 
therefrom.  The  butterflies,  however,  do  not  fly  very  long  distances, 
and  as  long  as  the  conditions  are  favorable  for  their  existence  on  one 
field  or  on  one  ranch  they  will  remain  there.  They  may,  however, 
fly  considerable  distances  when  forced  to  do  so  for  want  of  food  or 
for  fresh  green  alfalfa  on  which  to  deposit  eggs  or  when  driven  by 
the  wind,  and  thus  it  is  that  one  farmer  can  secure,  by  his  individual 
efforts,  such  remarkable  results  as  are  reported  below. 

RESULTS    OBTAINED. 

Of  the  ten  fields  cultivated  according  to  these  methods  only  one  was 
damaged  by  the  caterpillars  up  to  July  10,  the  date  on  which  so  large 
a  number  of  them  were  killed  by  the  disease  previously  mentioned. 
This  one  field  was  damaged  because  irrigation  had  been  delayed  for 
nearly  two  weeks  after  the  cutting  of  the  second  crop,  owing  to  a  new 
ditch  which  was  under  construction.  Being  a  thrifty  field  naturally, 
the  alfalfa  had  made  a  start,  assisted  by  the  moisture  still  present  in 
the  ground,  and  butterflies  coming  in  from  an  outside  field  deposited 
eggs  on  this  new  growth,  thus  enabling  the  worms  to  destroy  the  best 
of  the  crop  after  it  was  finally  irrigated.  As  a  result  almost  an  en- 
tire crop  was  lost.    A  field  adjoining  on  the  south,  which  had  been 

[Cir.  133] 


14  THE    ALFALFA    CATERPILLAR. 

irrigated  immediately  after  cutting,  was  not  in  tke  l§a^t  damaged. 
This  was  a  lesson  in  itself,  as  it  indicated  the  necessity  for  prompt 
work. 

I'ROTECTIVE    >IEASURES   ADVISED. 

Thus  from  a  comparison  of  observations  made  in  the  two  cksses  of 
fields  it. is  possible  to  derive  the  following  rules  for  handling  the 
crop : 

Do  not  abandon  a  field  because  the  caterpillars  are  beginning  to 
damage  a  hay  crop.  If  the  caterpillars  threaten  the  destruction  of  a 
crop  of  alfalfa  before  the  hay  can  possibl}^  mature,  mow  it  at  once, 
cutting  it  low  and  clean,  and  in  so  doing  starve  a  large  majority  of 
this  generation  of  worms,  thereby  protecting  the  next  crop  as  well  as 
saving  a  part  of  the  one  already  affected. 

Get  the  ranch  in  the  best  possible  cultural  condition.  Irrigate 
often  and  thoroughly  and  as  soon  after  cutting  as  the  crop  of  hay 
can  be  gotten  off  the  ground. 

Cut  close  to  the  ground  and  clean,  especially  along  the  ditch 
banks,  borders,  and  turnrows,  as  well  as  in  the  main  part  of  the  field. 

Cut  the  crojD  early.  AMien  just  coming  in  bloom  is  the  proper 
time.  Watch  for  caterpillars  in  the  early  spring  crop,  and  if  many 
are  observed  about  grown  cut  the  hay  a  few  days  before  it  is  in 
bloom,  and  thus  save  the  next  crop. 

Pasture  alfalfa  whenever  possible,  as  a  minimum  amount  of  dam- 
age occurs  in  such  fields. 

Use  the  methods  just  mentioned  on  early  spring  crops,  no  matter 
whether  any  worms  are  noticeable  or  not,  and  thus  avoid  any  risk  of 
haA  iiig  overlooked  them.  The  satisfactory  results  must  come  from 
an  application  to  an  early  crop. 

Renovate  every  winter,  either  by  disking  or  by  the  use  of  an  alfalfa 
renovator,  thus  disturbing  any  pupiv  that  may  be  wintering  over,  and 
putting  the  land  and  alfalfa  in  condition  for  good  growth  the  follow- 
ing spring. 

These  methods,  while  they  will  ])robably  be  of  value  in  other  sec- 
tions, have  been  tried  only  in  iho  Imperial  Valley  of  California,  and  . 
they  are  not   specifically   reconnnended   for  sections  where  climatic 
and  other  conditions  differ  from  those  found  in  this  valley. 

Approved.  university  of  florida^   ^^. 

•'■"'L"rj;,/. ,„,■,.«.„,.     liiiiiiLllli'' 

Washington,  D.  C,  January  26^  191L  ^  ^^ 

[Cir.  133] 

O 


